This invention relates generally to wireless communications, and more particularly, to performing in-situ calibration of a gain for a radio frequency (“RF”) radio receiver (“Rx”) using, for example, thermal noise as a calibrating signal.
Bipolar and Bipolar Complementary Metal Oxide Semiconductor (“BiCMOS”) are examples of processing technologies used to manufacture RF integrated circuits (“ICs”) that include RF receivers. Although these technologies provide for a relatively stable amplifier gain for an RF receiver over process, voltage and temperature (“PVT”), they are complex and expensive. Complementary Metal Oxide Semiconductor (“CMOS”) processing technology, which is simpler and less costly, has been implemented to avoid the complexities and costs of those technologies to manufacture RF ICs. But gains of RF receivers built in CMOS are not as stable as the above-mentioned technologies over PVT, thereby leading to large variations in amplifier gain. Consequently, the amplifier gain of a CMOS-based RF IC must be calibrated to ensure proper operation of the RF receiver.
FIG. 1 is a conventional system 100 for calibrating an amplifier gain for an RF IC 106. In this example, RF IC 106 is mounted on a substrate, such as a circuit board 104, as is a memory 110 and other ICs (not shown). To calibrate the gain of RF IC 106, system 100 includes a signal generator 112 connected to an antenna port 103 for providing a calibration signal 105 with which to determine the gain. Antenna port 103 is designed to receive antenna 102 after calibration. System 100 also includes a tester 108, which can be a computing device, for testing the gain of RF IC 106. Tester 108 receives an output signal 107 from RF IC 106 and then measures the gain with respect to calibration signal 105. If the gain deviates from a desired value, tester 108 generates calibration parameters for use by RF IC 106 to set the gain to a desired value. Tester 108 then stores these calibration parameters in memory 110, which is typically a programmable read-only memory such as an EEPROM. While functional, conventional communication RF IC calibration systems such as system 100 have several drawbacks. For example, system 100 is configured to calibrate amplifier gain at production and not in the field under normal operating conditions. The step of calibrating the gain during production is associated with increased costs and test times. Further, this calibration occurs usually once; calibration is not performed post-production. Other drawbacks of the conventional calibration techniques are that the initial calibration parameters do not generally account for either excursions in temperature or operational characteristics of the electrical components as those components age.
In view of the foregoing, it would be desirable to provide an improved calibration apparatus and technique that minimizes the above-mentioned drawbacks.